Just got emailed this from a mate that works for a telstra affiliate.
"From today, when you take up a Go Mobile $70 BYO or Casual plan we’ll now give you 4GB of Bonus Data. Add this to the 6GB of included data allowance and that’s a total of 10GB each month."
This apparently applies to New, Recontracting and even just changing your current non-contracted Telstra plan to it.
edit: So prior to today, the $70 BYO and Casual gave only 7GB I believe. Also for new customers the $10/month discount still applies when on a BYO plan.
Need link to page where deal can be seen ie telstra.com